Arvo testnets typically use Ropsten's deploy of the Azimuth contract
instead of mainnet's. This commit adds an 'arvo-ropsten' derivation for
Arvo as specialised to Ropsten.
In addition to using a different Azimuth address in %zuse, this also
configures %ames and :acme appropriately for running an alternate
network on Ropsten. %ames has its protocol version incremented, and
:acme uses the Let's Encrypt staging API.
Included here are derivations for creating brass and ivory pills using
arvo-ropsten, to boot.
Rather than conditional reconstructing the "urbit/bin/urbit-debug -g"
string everytime using the debug conditional, this information has been
added to the derivation's .meta attribute.
* Move extraneous stuff out of pkg/urbit/*
* s/urb/herb/g
* Removed some boilerplate for `urbit` builds.
* Build urbit tests and run them in the nix build.
